1. Field of the Invention
This invention relates generally to an improved design that provides better hydroplaning performance for a tire, and, more specifically, to a tire that has a variable pressure shear band located below its tread that provides increased structural stiffness to the tire, helping the tire to resist deformation when the tire encounters water, thereby decreasing the tendency of the tire to hydroplane. Advantageously, the variable pressure shear band can improve the hydroplaning performance and rolling resistance simultaneously without degrading wear performance.
2. Description of the Related Art
Those skilled in the art of pneumatic tires have developed a wealth of experience in adapting the tire construction to achieve a variety of performance combinations for tread wear, handling, wet and dry traction, rolling resistance, etc.
As an example of this adaptation, a pneumatic tire may be optimized for the vertical and tangential stresses in the tire's contact area between the outer surface (usually the tread) and the ground surface upon which the tire rolls. For example, good tread wear may be obtained when the vertical stresses between the tire and ground are uniformly distributed through the contact area and the tangential stresses are minimized. In particular, the tangential stress in the rolling direction should not change from strongly positive to strongly negative across the width of the contact area. However, to better improve the tire's resistance to hydroplaning on wet road surfaces, it is advantageous to have a higher vertical contact stress in the center portion of the contact area as compared to the shoulder, or lateral, portion of the contact area. This is usually achieved by adapting the tire construction or the curing mold transverse profile to obtain a transverse profile of the tire that is rounder than is desirable for optimized wear. In this case, the pneumatic tire will have an imbalanced tangential stress in the rolling direction, being significantly positive in the center portion and negative in the shoulder portion. Therefore, with the pneumatic tire, one skilled in the art has difficulty with optimizing the resistance to wear and resistance to hydroplaning simultaneously.
Non-pneumatic or structurally supported tires have been disclosed in the art. For example, U.S. Pat. No. 6,769,465, commonly owned by the Applicant of the present invention, relates to a structurally supported resilient tire that supports a load without internal air pressure. In an exemplary embodiment, this non-pneumatic tire includes a ground contacting portion and side wall portions that extend radially inward from the ground contacting portion and anchor in bead portions that are adapted to remain secure to a wheel during the rolling of the tire. A reinforced annular band is disposed radially inward of the ground contacting or tread portion. This shear band includes at least one shear layer, a first membrane adhered to the radially inward extent of the shear layer and a second membrane adhered to the radially outward extent of the shear layer. The invention of U.S. Pat. No. 6,769,465 provides several advantages including, for example, the ability to operate with partial or no inflation pressure and the flexibility to adjust the vertical stiffness of the tire somewhat independently of the ground contact pressure. This invention also provides a relatively well equilibrated contact pressure throughout the contact area.
By way of further example, U.S. Pat. No. 7,201,194, commonly owned by the Applicant of the present invention, also relates to a non-pneumatic tire. In an exemplary embodiment, this non-pneumatic tire includes an outer annular shear band and a plurality of web spokes that extend transversely across and radially inward from the annular band and are anchored in a wheel or hub. In certain exemplary embodiments, the annular shear band may further comprise a shear layer, at least a first membrane adhered to the radially inward extent of the shear layer and at least a second membrane adhered to the radially outward extent of the shear layer. In addition to the ability to operate without a required inflation pressure, the invention of U.S. Pat. No. 7,201,194 also provides advantages that include a more uniform ground contact pressure throughout the length of the contact area.
As described for the exemplary embodiments of the references discussed above, both used an annular shear band comprising a shear layer to provide desirable performance benefits in a tire. As described below, Applicants have discovered an advantageous construction for the shear layer and, in certain embodiments for the tread properties as well, that allows either wear or hydroplaning to be improved without degrading the other performance. In some cases, rolling resistance can also be improved. This improved construction for the shear layer and tread has application in pneumatic tires, non-pneumatic tires, hybrid tires that operate at reduced inflation pressure in conjunction with structural support from an annular band, and other products as well.